Some works [1]}, [2]}, [3]}, [4]}, [5]}, [6]}, [7]}, [8]}, [9]}, [10]}, [11]} focused on 2D upsampling, i.e. on increasing the width and height of CT/MRI slices, while other works [12]}, [13]}, [14]}, [15]} focused on 3D upsampling, i.e. on increasing the resolution of full 3D CT/MRI scans on all three axes (width, height and depth).
